Wood and/or cellulose based products exposed in an outdoor environment are biodegradable, primarily through attack by microorganisms. As a result, they will decay, weaken in strength, and discolor. The microorganisms causing wood deterioration include brown rots such as Postia placenta, Gloeophyllum trabeum and Coniophora puteana, white rots such as Irpex lacteus and Trametes versicolor, dry rots such as Serpula lacrymans and Meruliporia incrassata and soft rots such as Cephalosporium, Acremonium, and Chaetomium. In addition, wood is still subject to attack by wood-inhabiting insects, such as termites, beetles, ants, bees, wasps and so on. Wood preservatives are well known for preserving wood and extend the service life of wood products including decking boards, fence posts, utility poles, railroad ties, permanent wood foundation, and other cellulose-based materials, such as paper, plywood, particleboard, textiles, rope, etc., against organisms responsible for the deterioration of wood.
Utility poles and railroad cross ties are wooden structures that are traditionally pressure treated with wood preservative chemicals, such as chromated copper arsenate (CCA), pentachlorophenol, copper naphthanate or creosote. Pressure treatment with preserving chemicals can certainly prevent utility poles or railroad cross ties from fungal and termite attack and the pressure treatment can usually last for 30 to 40 years. However, the wood preserving chemicals can only penetrate through most of the sapwood portion of the wood species and rarely penetrate the heartwood portion. This will cause insufficient treatment and insufficient chemical absorption. In addition, improper treating practices may also cause poor treatment and insufficient chemical loadings. A direct consequence of the poor penetration and insufficient chemical loading is that, once the treated utility poles are placed in service, often times a small percentage of poles show early failure and subsequent strength loss. As a result, a supplemental or remedial treatment is needed to offer the protection for those poles that show early failures. In older poles, the preservative chemicals in the outer sapwood zone will gradually decline due to water leaching, ultraviolet degradation, chemical alteration or physical damage. As a result, external decay or termite attack may develop on the outer surface, and therefore there is an additional need for supplemental or remedial treatments to further extend the service life of aging utility poles and other wooden structures.
Preservative groundline treatments provide an economical extension to the useful life of utility poles. Experience has shown that groundline decay can be postponed almost indefinitely in cases where periodic inspection and maintenance programs are in effect. External treatments on utility poles and other wooden structures are typically applied below the ground level either as pastes or grease-type compositions that are brushed on the wood surface, and then covered with a moisture resistant barrier, or as self-contained ready-made preservative bandages. In both cases, the goal is to supplement the original preservative treatment to prevent or arrest surface decay. Protection is dependent upon the ability of the active ingredients to penetrate and remain in the treatment zone, and is limited to the depth of penetration. In addition, the composition must possess satisfactory physical properties, such as viscosity, spreadability, adherence, etc.
Historically, oilborne preservatives have been used for treating in-service utility poles and other wooden structures. Traditional oilborne preservatives included petroleum oils, creosote, copper naphthenate and pentachlorophenol. However, the use of oilborne supplemental preservatives is declining due to concerns of worker exposure to the organic solvents and leaching of the organic solvents into the environment. Furthermore, the organic solvents, including No. 2 fuel oil, have recently experienced unprecedented price increases making them cost prohibitive for the manufacture of supplemental/remedial wood preservative compositions.
Current, known commercially established preservatives for the after protection of in-service utility poles and other wooden structures contain copper or copper combined with boron and/or fluoride as their active biocides. Copper compounds, such as copper sulfate, copper carbonate and copper hydroxide, are generally known to be effective biocides as wood preservatives. Preferred copper compounds are generally insoluble and therefore must be solubilized to be effective in supplemental wood preservative compositions. This is typically accomplished by complexing the copper compounds with ammonia, acids or amines. Known copper complexes used in the field of wood preservation include copper naphthenate, water-dispersible copper naphthenate, copper ethanolamine, ammoniacal copper citrate, alkaline copper quaternary and others. Sodium fluoride and sodium borate are the most commonly used biocides in remedial preservative compositions. The sodium salts of boron and fluoride are able to penetrate further through the wood structure due to their water solubility and mobility.
Although prior art compositions for the remedial treatment of utility poles and other wooden structures have been shown to be effective in extending the useful life of wood products in-service, there are several problems that exist with current preservative compositions.
One limitation of using oil or water dilutable copper complexes is that they can readily leach from wood. Leaching of copper from wood can be further increased by the presence of oil solvents present in utility poles or cross ties from initial treatment with pentachlorophenol, creosote or copper naphthenate. Elevated moisture levels commonly found within in-service poles and ties, particularly near or below groundline, can also increase the leaching rate of water dilutable copper complexes found in current preservative paste compositions.
The leaching of the copper component from current paste compositions is a concern from both a performance and environmental perspective. Depletion of the copper by leaching will ultimately compromise the long term bioefficacy of the supplemental or remedial formulation, and the leached copper causes concern that the environment surrounding the treated structure will be contaminated. It has been established that copper is extremely toxic to fish and other aquatic organisms at very low concentrations. Concerns over copper leaching from supplemental wood preservative compositions are such that their use is often limited or even restricted in areas of standing water or near water ways.
In addition, the copper component of current supplemental wood preservative compositions is not protective against some species of copper-tolerant wood decay fungi, often located in the Gulf-Coast region of the U.S. Generally, higher loadings of copper are required in remedial compositions containing soluble forms of copper and/or a co-biocide is incorporated into the composition to afford protection against copper-tolerant decay fungi.
Another concern with current copper containing paste compositions is worker exposure when applying to in-service wooden structures. Copper complexes formed with the use of amines such as monoethanolamine, ethylenediamine and the like, acids such as, for example, naphthenic or arsenic acid and ammonia can be corrosive to human eyes and skin and may be fatal if ingested. As a result, personal protective equipment required by personnel applying current remedial compositions can be costly, cumbersome and may interfere with the correct application of the material to an in-service wooden structure.
Finally, complexing copper to impart solubility can be expensive. Generally, high levels of the complexing agents are required to solubilize copper compounds. For example, 2 to 4 moles of monoethanolamine are required to complex 1 mole of copper and 4 moles of ammonia are needed to complex 1 mole of copper. This can add considerable cost to the formulated remedial preservative compositions. In addition, oilborne copper naphthenate and other oil-based compositions generally require the use of No. 2 fuel oil as a carrier and are therefore extremely susceptible to large variations in cost.
Examples of supplemental or remedial preservative compositions for the afterprotection of wood in-service can be found in the following literature.
U.S. Pat. No. 5,342,438 to West discloses a non-water dilutable remedial wood preservative containing copper derived from an amine-inorganic copper complex, combined with at least one sodium salt selected from the group consisting of sodium borate and sodium fluoride in a ratio of 2 to 120 parts of the sodium salt for each part of copper in the preservative.
U.S. Pat. No. 6,110,263 to Goettsche teaches a process for the afterprotection of wood, which comprises treating the wood with and effective wood preserving amount of a wood preservative composition comprising a copper compound, a polyamine or alkanolamine having at least two nitrogen atoms, and an inorganic fungicide, the treatment being effected by means of a bandaging process, an inoculation injection process, a borehole process or a paste process.
U.S. Pat. No. 5,084,280 to West claims a paste composition for preserving wood which contains as its only active wood preservation ingredients a mixture of 10-90% by weight of a water-dispersible copper naphthenate and 90-10% by weight of borax.
U.S. Pat. No. 6,352,583 to Goettsche discloses a wood preservative for the supplemental protection of wood, consisting essentially of one or more copper compounds, one or more alkanolmonoamines and one or more complexing organic carboxylic acids or ammonium or alkali metal salts of said complexing organic carboxylic acids.
U.S. Pat. No. 6,306,202 to West teaches a water soluble fixed copper-borax wood preservative composition which comprises a fixed copper compound selected from the group consisting of copper oxides, copper hydroxide, basic copper carbonate, basic copper sulfate, and copper oxychloride combined in water with sodium tetraborate decahydrate wherein the fixed copper compound concentration ranges from 0.01 parts to 0.20 parts for each part of sodium tetraborate decahydrate.
This invention discloses a supplemental or remedial wood preservative composition which solves the problems identified with current, known compositions and addresses the need for a more environmentally friendly technology for the afterprotection of in-service wooden structures. This need is solved by the subject matter disclosed herein.